INFLUENCE OF MEMBRANES UPON OSMOTIC CURRENTS. 483 



and examine all the properties of animal membranes, both 

 within and without the living organism. 



In the first place, is there any proof that all membranes 

 which will admit the passage of liquids are porous ? This 

 is a most important question ; and it lies at the foundation of 

 the explanation of the phenomena of endosmosis by the laws 

 of capillary attraction. 



In all membranes which possess an anatomical structure 

 discoverable by the microscope, there are undoubtedly inter- 

 stices between the fibres, cells, etc., of which the tissue is 

 composed ; but on the other hand, animal membranes gen- 

 erally have a layer, like the basement-membranes of mucous 

 tissues, which is absolutely homogeneous and structureless. 

 In applying the laws of endosmosis to physiological absorp- 

 tion, it is found that the membranes which are most easily 

 penetrated by fluids are excessively thin and perfectly homo- 

 geneous. Take, for example, the walls of the capillary blood- 

 vessels, through which the greatest part of the physiological 

 absorption takes place ; this membrane is from jj^oo- to Tsio-ir 

 of an inch thick, and is entirely amorphous, with the excep- 

 tion of a few oval nuclei imbedded in its substance. The as- 

 sumption that invisible capillary orifices exist in these thin 

 amorphous membranes is purely hypothetical, and is unwar- 

 rantable. The only circumstance which could lead to such 

 a supposition is the fact that these membranes can be pene- 

 trated by liquids. 



It is manifestly unphilosophical and absurd to offer, as an 

 explanation of endosmosis through structureless membranes, 

 an hypothesis which has its only support in the existence of 

 the phenomenon which it is intended to explain. This mode 

 of reasoning is all the more unsound, as the phenomena of 

 endosmosis are very far from being completely understood ; 

 and many important properties of organic structures, which 

 bear directly upon the question under consideration, are ig- 

 nored. For example, physiological absorption does not 

 always take place in accordance with known physical laws. 



